Fermented food products have been developed and used by mankind with the aid of lactic acid bacteria (LAB), which have been classified as probiotics and are categorized as generally recognized as safe (GRAS) by the United states Food & Drug Administration (USFDA). In addition to be considered as the powerhouses for the food industry, LAB continue to be the focus of considerable interest as probiotic organisms, since they have also been conferred with specific health promoting functions which they execute by modulating the gut environment of the host.
Their ability to adhere to certain areas of the gastrointestinal tract has created interests to tap the potential of such microbes as vehicles for the delivery of biologically active compounds & vaccines (Pouwels et al., Int J Food Microbiol., 1998, 41, 155-157).
Most infectious organisms gain entry at the mucosal surfaces, there is a great deal of interest in developing vaccines that elicit effective mucosal immune responses against various pathogens. LAB, which are safe and nonpathogenic, are excellent mucosal delivery vehicles for heterologous antigens and therapeutic proteins. Many LABs produce extracellular polysaccharides and these have been extensively studied in terms of their biosynthesis, structure & function and engineering, including the importance of these molecules in host microbe interactions (Leeber et al., Microbial Biotechnology, 2011, 4(3), 368-374).
Camelids produce functional antibodies devoid of light chains of which the single N-terminal domain is fully capable of antigen binding and could be delivered on mucosal surfaces by the lactic acid bacteria for various therapeutic interventions. The unique physicochemical and pharmacological properties of these camelid heavy chain antibody (VHH) fragments have led to its prospective use as new generation therapeutic agents. The remarkable preference of VHH fragments to bind clefts and cavities on protein surfaces offers the possibility to develop selective therapeutics (Paalanen et al., Eur J Pharm Sci., 2011, 42(4), 332-9) by activity modulation of cell surface proteins, such as receptors, ion channels involved in various biological activities (Wei et al., PLoS ONE, 2011, 6(12). Moreover, VHH fragment molecules recognize cryptic epitopes hidden deeply in clefts of various pathogens (Forsman et al., J. Virol., 2008, 82(24), 12069-12081) and have high structural stability and solubility (Muyldermans et al., Biochem Sci., 2001, 26, 230-235; Philipp et al., Nat. Biotechnol., 2005, 23(9), 1126-1136).
Salmonellosis is the most common food borne disease and gastrointestinal infection across the world. Salmonella is the second major cause of food borne diseases in U.S., Europe & in the world causing as many as 1.3 billion cases of diseases annually. In addition to the health consequences, Salmonella species with about 2600 existing serovars are being identified belonging to six subspecies (Coburn et al., Immunology and Cell Biology, 2007, 85, 112-118; Ochman et al., EXS, 1994, 69, 479-493). Sub species are further sub divided into serovars that are differentiated by their flagellar, carbohydrate and lipopolysaccharide (LPS) structures. S. enteric species are typically orally acquired pathogens that cause one of the four major syndromes, Enteric fever (typhoid) enterocolitis/diarrhea, bacteremia and chronic asymptomatic carriage. The disease manifestation depends on both host susceptibility and the infectious. S. enteric serovar (Fierer et al., J Clin Invest., 2001, 107, 775-780). Prominent inflammatory disease outcomes are a common feature of typhoid & enterocolitis. The various patho-biological outcomes of infection are mainly due to the interaction of the Salmonella species with host defence mechanisms at various tissues in different stages of infection. This results in significant host immunopathology, morbidity and mortality.
Salmonella is a significant pathogen for food producing animals and these animals are the primary source of salmonellosis. It is one of the most commonly isolated food borne pathogens associated with poultry, raw meats, eggs, milk and dairy products, fresh farm produce like fruits & vegetables etc. In recent years, the incidence of food borne outbreaks caused by the contamination of fresh fruits and vegetables has increased and become a great concern in industrialized countries.
The major types of vaccines used to control salmonellosis are the killed bacteria vaccine, subunit vaccines and live attenuated vaccines. Comparative analysis of live and killed vaccines revealed that killed vaccines are usually less effective as they comprise of surface antigens that give rise to inadequate protective immune response, they fail to elicit secretory immune response at the mucosal surfaces which is critical in inhibiting the colonization of the pathogens at the mucosal surface. Attempts to overcome all these shortcomings by the use of various adjuvants has led to only partial success (Smith, J Hyg., 1956, 54, 419-432; Singh et al., Haryana Vet., 2005, 44, 1-12; Baljer et al., J Med Vet., 1986, 33, 206-212).
The utility of live vaccines in eradication of salmonellosis is limited, as there are multiple serovars of Salmonella and vaccines made from any one serovar do not confer cross protection against another serovar. The organisms are capable to adapt in different animal species whilst still maintaining their zoonotic and interspecies transfer potential. Moreover, effective vaccines against some host adapted and common serovars in the primary source of host have been developed but their use has led to the emergence of other serovars. This has been further compounded by the international trade and movement of animal and farm products which has led various serovars to cross continental boundaries. Thus, there is a need in the art to develop anti-Salmonella biological and it is desirable to develop and provide an alternative means for the control and management of enteropathogenic Salmonella, by therapy and/or prophylaxis.
EP1066375B1 relates to use of transformed Lactobacillus species as vaccine delivery vehicles.
US2008/0206233 A1 relates to heavy chain immunoglobulins or fragments thereof of the VHH or VNAR type or domain antibodies (dAbs) suitable for use in the management of infections, particularly of the gastrointestinal tract.
US2009/0226418 A1 relates to food products or pharmaceutical preparations comprising antibodies or antibody fragments which are active in the gut and probiotic microorganisms independent from their antibodies or antibody fragments.